1. Field of the Invention
This invention relates to the preparation of predominantly noncyclic polyalkylene polyamine products and more particularly pertains to a direct liquid phase catalytic process for synthesizing predominantly noncyclic trialkylenetetramines and higher odd alkylene homologs with low heterocyclic amine content.
2. Prior Art
Heretofore, polyalkylene polyamine compounds and particularly polyethylene polyamine compounds such as diethylenetriamine, triethylenetetramine, and the higher homologs as well as the related carbon-substituted homologs have been conventionally produced by reacting an alkyl halide, e.g., ethylene dichloride, with an amine compound such as ammonia, ethylenediamine, and the like at elevated temperatures and pressures. Generally speaking, relatively high yields of predominantly noncyclic polyethylene polyamine compounds are obtained along with varying yields of heterocyclic amines, e.g., piperazine materials. These processes, while generally employed throughout the industry, suffer from serious disadvantages.
Exemplary shortcomings of these procedures include large amounts of energy required to produce the reactants and expensive recovery procedures. The resultant hydrohalide salts of ammonia and the polyamines must undergo caustic neutralization to obtain the free polyamines. Separation of the desired free polyamines is difficult and disposal of the polluting by-products, such as the alkali metal halide salt, is expensive. Additionally, the products produced possess undesirable colorants, limiting use of the material in color-critical applications.
There are several procedures described in the literature for directly preparing predominantly noncyclic polyethylene polyamines by the condensation reaction of an aminoalkanol compound and an alkylatable amine compound which do not require neutralization of the reaction product to obtain the desired salt-free polyamines. For example see U.S. Pat. No. 3,714,259.
It has also been previously disclosed that certain phosphoric acid compounds are effective as catalysts in promoting condensation reactions between several types in amines, and aminoalkanols generally. The reaction conditions are relatively mild and/or the condensation sites are limited. For example, U.S. Pat. No. 3,121,115 to Meuly teaches a process for aminoalkylating certain amines having a replaceable amino hydrogen, particularly aromatic primary and secondary amines, which includes heating the amine compound with an N-tertiary aminoalkanol at from 150.degree. to 250.degree. C in liquid phase with continuous water removal in the presence of a phosphoric acid compound.
We have now discovered an improved catalytic process whereby predominantly noncyclic polyalkylene polyamines and particularly trialkylenetetramines and higher odd alkylene homologs such as pentalkylenehexamines may be selectively produced as the condensation product of a diol compound and preferably an alkylene diol compound, with an alkyleneamine compound under economically feasible short reaction times. The improved process provides conversion rates of reactants and selectivity comparable to or higher than those obtained by conventional processes which require neutralization with alkali, as described hereinbefore. In addition, condensation to selective alkyleneamines is possible by choosing appropriate diol reactants.
Surprisingly, it has been discovered that the condensation reaction may be carried out under rather severe processing conditions, such as temperatures above about 250.degree. C in liquid phase without the expected decomposition and excessive by-product formation. For example, it is known that polyalkylene polyamines, and particularly the higher homologs of the ethylene amines such as triethylenetetramine, tetraethylenepentamine, etc., are thermally degradable. Moreover, experiments have shown that total reactants conversion is improved under these processing conditions while selectivity is substantially maintained as compared to the use of less severe processing conditions.
The process of the instant invention is further surprising in light of the disclosure that the vapor phase reaction involving ethylenediamine compound and a polyhydric alcohol in the presence of a thorium sulfate catalyst yields only the corresponding N-alkylated amine compound and not the polyalkylene polyamines. See for example U.S. Pat. No. 3,732,311.